Large voltage drop when using blower motor: Time to replace motor?

[cleithau]

When I turn on my heater in the morning I notice a fairly significant voltage drop when I turn on the blower motor. Under 12V when at idle, new alternator, new batteries, with the blower motor off voltage is fine. Or driving with the blower motor on its about 12.5 volts. Doesn't seems to blow as much air as a couple years ago? Is there a test for the blower motor?

 

[RKOCH]

Nope replace it and it will do the same thing. Ford goofed on wiring that one you need to do the relay mod and all will be fine.

 

[Mr_Roboto]

Yea the blower motor is one of the biggest draws, sounds like you have a shorted winding which is drawing additional current.

 

[RKOCH]

I put 2 new ones in and it did the same thing and did the mod and have twice the fan speed.

 

[Diesel JD]

So is the blower on that same relay that has the headlights and the glow plugs(on the 83-86)? Do you mean the headlight relay mod or something else. My motor barely works, don't know if it is drawing way too much current or not.

 

[The Warden]

As I understand it, at least on the '80-'86 trucks, the blower does not have a relay at all. For once in my life, I agree with RKOCH that doing the "relay mod" will help to improve your fan blower speed.

That said, that does not mean that your blower is in good shape. Based on what you said about the blower not seeming to put out as much air as it has in the past, I'll bet that your blower's bearings are getting dry and trying to seize up. I would pull the blower (simple to do from under the hood) and see how freely the fan spins. If it feels like there's too much resistance, you can use some WD-40 or 3-in-1 oil or white lithium grease to spray into the bearings. That should free it up some, but in my experience, that's really only a temporary fix...I would plan on replacing the blower motor. I sprayed the bearings in my motor just under 2 years ago, and my fan output's dropped noticeably in that timeframe...it's getting to be time for me to shell out the $$ to get a new blower...

 

[EMD_DRIVER]

Is there anything written up on this mod?

Gary

 

[Diesel JD]

I'd like to know more about it as well, where is the blower motor located anyway?

 

[EMD_DRIVER]

I'd like to know more about it as well, where is the blower motor located anyway?

Passenger side of the firewall. Ya can't miss it..

Gary

 

[BigRigTech]

Fire a new one in there and try it....Mine moves lots of air with out the mod...I have about 6 of those motors kicking around - big seller in the fall/winter...

 

[The Warden]

Is there anything written up on this mod?

Gary

http://oilburners.net/forums/showthread.php?t=24777

AFAIK, that's the only place on this site that it's been discussed...

 

[DarkwingDork]

As I understand it, at least on the '80-'86 trucks, the blower does not have a relay at all. For once in my life, I agree with RKOCH that doing the "relay mod" will help to improve your fan blower speed.

80-90 deffinately don't have the relay. Plan on doing that mod, will write a tech article for it. I'll post a link to my website as soon as i get the kinks ironed out of apache...it's all about mods to IDI motors and other parts of our trucks. Later!
~Jon

 

[The Warden]

Plan on doing that mod, will write a tech article for it. I'll post a link to my website as soon as i get the kinks ironed out of apache...it's all about mods to IDI motors and other parts of our trucks.

Are you planning on using a separate switch (as was described in the other thread), or do you want to wire it into the factory switch? I haven't figured out the wiring, but I THINK that it can be done with the factory switch, to keep everything looking original inside the cab.

BTW, cool idea re: the webpage! I've been trying to do the same for 3 years now...I've got something up, but it's nowhere near as organized or complete as I'd like. I'll have time someday...

 

[DarkwingDork]

I going to use the factory switch. From the looks of the diagram, positive current goes from the fuse panel, through the heat select switch (closes circuit in all positions except off) then flows to the blower motor. The blower switch passes current either through one of the circuits on the resistor (low, medium, and medium-high) or through the switch and straight to ground.

I think we need two relays: 1 triggered by the heat select switch to give positive from the battery to the blower motor and another between the "high" terminal on the switch and ground.

Alternatively, you could eliminate the second relay by adding a larger ground to the blower motor switch and running it back to the battery. I'll do some tinkering and report my findings. There WILL be a tech article!

In other good news, I just got the website back online!! give it a visit http://dynamicidentity.us/

 

[adrianspeeder]

No, only need one relay. Pretty sure I wrote this up already on here with the diagram. I'll look for it after work.

For the 80-86...

Pull power from the heater select switch to pin 86 of a SPST relay, then connect pin 85 to ground. Run a 12g from the battery through a 20amp fuse, through pin87. Pin 30 goes to the hot side of the blower motor. The ground of the motor is what goes through the speed switch and ground and/or resistors on the lower settings.

'87-'88 are a little different. Simply need a key on hot wire to go to pin 86 of the relay.

Adrianspeeder